1. Technical Field
The present invention relates to a lead pin for a package substrate and a method for manufacturing a package substrate with the same, and more particularly, to a lead pin for a package substrate capable of improving bonding reliability with the package substrate and a method for manufacturing a package substrate with the same.
2. Description of the Related Art
With the development of the electronics industry, various types of semiconductor packages have been manufactured. Recently, a package substrate in a Pin Grid Array (PGA) type mounted with a plurality of T-type lead pins has been prevalently used, as a substrate that connects a package substrate, on which an integrated circuit (IC) is mounted, to a main board.
As a lead pin used in a general package substrate, an insertable lead pin where a pin is inserted into a hole formed on the package substrate and a T-type lead pin that is attached to a package substrate by soldering have been prevalently used. However, the T-type lead pin has gradually become widespread due to less limitation in a circuit configuration of a package substrate, as compared to the insertable lead pin.
However, the T-type lead pin has disadvantages in that the lead pin is inclined or it is difficult to maintain uniform bonding strength. In particular, as the use of lead has been recently limited in consideration of the environment, a solder (Sn—Ag—Cu, and Sn—Sb) not using lead has been used, but the melting temperature of the solder is increased. In this case, a solder for connecting lead pins that support the lead pins is melted by reflow heat during a reflow process for mounting an IC chip on a package substrate, thereby causing inclination of the lead pins. In addition, voids are generated between a head part of the lead pin and the solder at the time of soldering the existing T-type lead pins, and as a result, the bonding reliability of the lead pins is deteriorated.
The foregoing problems of the related art will be described below in detail with reference to FIGS. 1 and 2.
FIG. 1 is a diagram showing one example of a configuration in which a lead pin is bonded to a package substrate according to the related art, and FIG. 2 is a diagram showing another example of a configuration in which a lead pin is bonded to a package substrate according to the related art.
Referring to FIGS. 1 and 2, after a solder paste 12 is applied to a pad part 11 of a package substrate 10, a lead pin 20 is disposed on the pad part 11 of the package substrate 10 so that the head part 21 of the lead pin 20 contacts the pad part 11 thereof. A reflow process of bonding the plurality of lead pins 20 to the pad part 11 of the package substrate 10 is performed. Therefore, the package substrate 10 to which the lead pins 20 are bonded is manufactured.
However, voids 13 may be generated in the solder paste 12 during the process of applying the solder paste 12 to the pad part 11. These voids 13 deteriorate the bonding strength of the lead pin 20 when the lead pins 20 are bonded to the package substrate 10. In addition, as shown in FIG. 2, there is a problem in that the lead pin 20 inclines to one side as the voids 13 are discharged from the solder paste 12.
In addition, a solder paste (Sn95-Sb5, melting point 232 to 240° C.) for bonding the lead pins 20 has a relatively higher melting point, as compared to the solder paste (Sn96-Ag3, 5-X solder, melting point 221° C.) for bonding the IC chips. Therefore, in order to bond the lead pins 20 to the package substrate 10, the reflow process should be performed under a relatively higher temperature condition. However, the reflow process under the high-temperature atmosphere cannot help but be controlled to a shorter time when heating is performed at the temperature exceeding the melting point in order to minimize thermal impact applied to the package substrate 10. Therefore, since the time for the voids 13 to discharge from the solder paste 12 is insufficient, the melting surface of the solder paste 12 itself becomes non-uniform or the tension with the lead pin 20 is caused by the expansion of the voids, such that the reflow process causes the phenomenon where the lead pin 20 is inclined to one side.